Selective Single‐Site Pd−In Hydrogenation Catalyst for Production of Enhanced Magnetic Resonance Signals using Parahydrogen

Pd−In/Al2O3 single‐site catalyst was able to show high selectivity (up to 98 %) in the gas phase semihydrogenation of propyne. Formation of intermetallic Pd−In compound was studied by XPS during reduction of the catalyst. FTIR−CO spectroscopy confirmed single‐site nature of the intermetallic Pd−In phase reduced at high temperature. Utilization of Pd−In/Al2O3 in semihydrogenation of propyne with parahydrogen allowed to produce ≈3400‐fold NMR signal enhancement for reaction product propene (polarization=9.3 %), demonstrating the large contribution of pairwise hydrogen addition route. Significant signal enhancement as well as the high catalytic activity of the Pd−In catalyst allowed to acquire 1H MR images of flowing hyperpolarized propene gas selectively for protons in CH, CH2 and CH3 groups. This observation is unique and can be easily transferred to the development of a useful MRI technique for an in situ investigation of selective semihydrogenation in catalytic reactors.